1. Field of the Invention
The present invention relates to an imaging lens system for forming an image of a subject and an imaging apparatus using the imaging lens system.
2. Description of Related Art
Generally, a small-sized, lightweight, and wide-angle imaging lens system with antiweatherability has been known, which is used in an imaging apparatus for an on-vehicle camera, a portable cellular phone camera, a surveillance camera, or the like. Such an imaging lens system forms an image of an object to be a target subject on a light receiving surface of an imaging device such as a CCD element or a CMOS element.
A small-sized, lightweight, and wide-angle imaging lens system formed of six lenses also has been known. As the known wide-angle imaging lens system formed of six lenses, an imaging lens system in which a spherical lens made of glass is used in the third lens from the object side has been known (refer to JP-A-2007-249073). In addition, an imaging lens system formed of five or six lenses including a plastic cemented lens has been known (JP-A-2006-284620). There are inventions disclosed in JP-A-2009-92797 and JP-A-2009-92798.
However, in the inventions disclosed in JP-A-2007-279073 or JP-A-2009-92798, the third lens can be made of glass. This causes an increase in cost. Further, by using an aspheric lens for the third lens, it is possible to satisfactorily correct field curvature additionally.
The lens system disclosed in JP-A-2006-284620 uses a cemented lens formed by cementing plastic aspheric lenses. When an aspheric lens is used in the cemented lens, manufacturing costs increase.
In recent years, imaging devices such as CCD elements and CMOS elements have been improved greatly in miniaturization and an increase in the number of pixels. Accordingly, imaging lens systems used in imaging apparatuses for an onboard camera, a mobile phone camera, a surveillance camera, and the like are required to achieve an increase in angle of view, reduction in size, and a decrease in aberration.